While the present invention may find application in a wide variety of tire testing apparatus wherein it is necessary to rapidly chuck tires it is applicable to great advantage in tire uniformity testing machines. Tire uniformity testing machines commonly include an upper rim, a vertically-movable lower rim, and a conveyor to bring a tire between the upper and lower rims. A mechanism is provided to raise the lower rim through an opening in the conveyor, carrying a tire with it, to the upper rim where the tire is inflated. The lower rim carries a center cone that is engagable with a center recess in the upper rim, the cone precisely positioning the upper rim with respect to the lower rim so that the separation between the two is at the desired bead width for the tire being tested. A motor is connected to the upper rim to rotate it at a predetermined test speed. A load wheel or road wheel, rotatable on an axis parallel to the axis of the tire, is movable into engagement with the tire tread so as to load the tire as it rotates in a manner simulating a road condition.
A hydraulic actuator is connected to the lower rim to raise and lower it. This actuator must be capable of applying a force sufficient to overcome the separation force of tens of thousands of pounds acting on the rims when the tire is inflated. The force applied by the actuator must also be sufficiently great to hold the cone against the recess of the upper rim with sufficient pressure to driveably couple the upper and lower rims so that the rotational force applied to the upper rim is transmitted to the lower rim through the center cone rather than through the tire substantially without slip which might otherwise distort the tire and possibly affect test results.
The problem that the existing machines present is the need to quickly change the machine over to accommodate tires of different bead widths. The bead width is the spacing between the two opposed beads by which the tire is seated on the respective rim halves when the tire is properly mounted. With modern tire production practices one may no longer rely on being able to test a relatively large batch of tires of a given bead width. To the contrary, tires presented to the testing machine conveyor often now have different bead widths from one tire to the next.
The practice prior to the present invention has been to adjust bead width by removing the cone from a socket in the lower rim assembly and to replace it with one of a different length as to create a different bead width when the new cone is in engagement with the conical seat of the of upper rim. Such a system is costly and inefficient because it requires stopping the machine for manual changeover each time a tire with a different bead width is presented for testing. It also requires an operator to reach into the machine to perform the spindle change.
Another significant problem inherent in the prior art is that of insuring proper seating of the tire bead on the rim during inflation. When the lower rim engages the tire, gravity normally insures close engagement of the lower bead with the lower rim. However, when the nose cone of the lower rim bottoms out in the socket of the upper rim, a significant gap often remains between the upper bead of the tire and the upper rim due to the natural tendency of the tire to sag under the force of gravity in its uninflated condition. This problem is most apparent in the case of tires having wide bead widths where the gap between the top rim and the top bead is generally larger. The system relies on the inrush of a large flow of inflation air to pressurize the interior of tee tire sufficiently to overcome this sag to lift the bead into engagement with the rim to seat upon it. Often, this does not occur properly.